Instruments and techniques for spinal disc space preparation

ABSTRACT

A milling instrument assembly ( 15 ) is provided for vertebral endplate preparation along a cutting path obliquely oriented to the axis of approach to the vertebra. The milling instrument assembly ( 15 ) provides control of the anterior-posterior depth of endplate removal by guiding cutting assembly ( 120 ) in the disc space as it moves transversely across a housing assembly ( 16 .) Methods and techniques are included for using the milling instrument assembly ( 15 ) in spinal surgery.

BACKGROUND

[0001] Implants of various types have been utilized throughout the bodyfor various orthopedic bone applications, including application in thefield of preparing an intervertebral disc space to receive an interbodyfusion device to create bony fusion or a spacer providing artificialdisc functions. Such procedures may be necessary where the natural dischas degenerated or slipped resulting in pain and discomfort to apatient. The deterioration or movement of the disc often results in thetwo adjacent vertebral bodies coming closer together. A common treatmentis to surgically restore the proper disc space height to therebyalleviate the neurologic impact of the collapsed disc space. Typically,the damaged disc is removed and a load bearing structure, eitherman-made or natural, is inserted to maintain the disc height and promotebony fusion and/or restore motion between the adjacent vertebrae.

[0002] Prior instruments and techniques for disc space preparation havebeen provided to prepare a disc space for insertion of an interbodyimplant. For example, milling devices have been provided to remove bonefrom a vertebral endplate. Milling devices can intrude on the otheranatomical structures of the vertebra other than the endplate, such asthe posterior elements of the vertebra where the spinal cord is located.There remains a need for instruments that reduce intrusion on theanatomical structures of the vertebra other than the endplate duringpreparation of the disc space for receipt of an implant.

SUMMARY

[0003] The present invention relates generally to instruments andtechniques for preparing a site between two adjacent bony segments froman anterior oblique approach to receive an implant therebetween. Thepresent invention further relates generally to instruments andtechniques for vertebral endplate preparation along a path obliquelyoriented to the axis of approach to the vertebra.

[0004] In one aspect of the invention, an instrument is provided thatincludes a housing positionable adjacent the spinal disc space. Theinstrument includes a block proximal the housing. A cutting assemblyextends through the block and into the housing. When inserted, theinstrument has a longitudinal axis extendable from the spinal column.The cutting assembly is guidable with the block along a cutting pathextending transversely to the longitudinal axis. At least a portion ofthe cutting path extends obliquely to the longitudinal axis.

[0005] Another aspect of the invention contemplates an instrument havinga housing assembly positionable adjacent a vertebra. The instrumentincludes a cutting assembly extendable through the housing assembly.When positioned adjacent the vertebra, the instrument includes alongitudinal axis extending from the spinal column. The cutting assemblyis guidable along a guide surface of the housing assembly. The guidesurface extends transversely to the longitudinal axis. At least aportion of said guide surface extends obliquely to the longitudinalaxis.

[0006] In a further aspect of the invention, an instrument includes ahousing assembly positionable adjacent a vertebra. The instrumentincludes a cutting assembly extending through the housing assembly. Theinstrument includes a longitudinal axis extending from the spinal columnwhen the housing assembly is positioned adjacent the vertebra. Theinstrument includes means for guiding the cutting assembly relative tothe housing assembly along a cutting path. At least a portion of thecutting path extends obliquely relative to the longitudinal axis.

[0007] The invention further contemplates a method of disc space andendplate preparation from an anterior oblique approach to the spine. Inone aspect, the method includes gaining access to the spine andinserting a cutting assembly into the spinal disc space from an anterioroblique approach. The method includes guiding the cutting of one or bothof the endplates along a cutting path having a first portion extendingorthogonally to the direction of the approach and another portionobliquely oriented to the direction of the approach.

[0008] In another aspect, the method includes gaining access to andinserting a cutting assembly into the spinal disc space from an anterioroblique approach. The method also includes guiding the cutting of one orboth of the endplates along a cutting path in the disc space, at least aportion of which extends obliquely to the angle of approach to the discspace.

[0009] These and other aspects will also become apparent from a reviewof the accompanying drawings and descriptions thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a side view of a spinal column segment and a millinginstrument assembly positioned adjacent thereto in an anterior obliqueapproach.

[0011]FIG. 2 is a plan view of the spinal column segment and millinginstrument assembly of FIG. 1.

[0012]FIG. 3 is a sectional view looking at the side of the spinalcolumn segment and milling instrument assembly of FIG. 1.

[0013]FIG. 4 is a perspective view of a vertebral body showing a millingpattern in an endplate thereof provided by the milling instrumentassembly of FIG. 1.

[0014]FIG. 5 is a perspective view of a guard tube attached to a housingof the milling instrument assembly of FIG. 1.

[0015]FIG. 6 is a perspective view of the milling instrument assembly.

[0016]FIG. 7 is an exploded perspective view of the milling instrumentassembly of FIG. 6.

[0017]FIG. 8 is a side elevation view of the milling instrument assemblyof FIG. 6 rotated 180 degrees about its central axis so that it isupside down relative to FIG. 6.

[0018]FIG. 9 is a section view through line 9-9 of FIG. 8 with thecutting assembly of the milling instrument assembly in a first position.

[0019]FIG. 10 is the section view of FIG. 9 with the cutting assembly ina second position.

[0020]FIG. 11 is an enlarged view of a portion of the milling instrumentassembly of FIG. 9.

[0021]FIG. 12 is an enlarged view of a portion of the milling instrumentassembly of FIG. 10.

[0022]FIG. 13 is a perspective view showing the milling instrumentassembly of FIG. 6 with the cutting assembly in the first position.

[0023]FIG. 14 is a perspective view showing the milling instrumentassembly of FIG. 6 with the cutting assembly in the second position.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0024] For the purposes of promoting an understanding of the principlesof the invention, reference will now be made to the embodimentsillustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended. Any such alterationsand further modifications in the illustrated device, and any suchfurther applications of the principles of the invention as illustratedherein, are contemplated as would normally occur to one skilled in theart to which the invention relates.

[0025] The present invention relates to instruments and methods forgaining access to a disc space between adjacent vertebral bodies,distracting the disc space to a desired height, preparing the disc spaceto receive an implant to maintain disc space height and angulation, anda method for inserting an implant into the prepared disc space. Morespecifically, while methods and instruments disclosed in the presentapplication may have application in other areas of the spine or thebody, it is specifically contemplated that the present instruments andmethods may be utilized in preparation of an obliquely oriented site onan endplate of a vertebra. An anterior-oblique approach to the spine maybe desirable in certain areas of the spine where a direct anteriorapproach is difficult or impossible because of patient anatomy. Otherapproaches, including direct anterior and lateral approaches, are alsocontemplated. The term implants in the present application is used in abroad sense to encompass both implants constructed of man-madematerials, as well as implants formed of naturally occurring materials.Further, implants contemplated to be used with the present invention mayinclude those intended to promote fusion between adjacent vertebra aswell as artificial disc replacements.

[0026] Referring to FIG. 1, there is shown a milling instrument assembly15 positioned adjacent spinal column segment 200. Milling instrumentassembly 15 can be positioned adjacent the disc space of adjacentvertebrae in a patient, and used by the surgeon to prepare one or bothof the endplates of the adjacent vertebrae to receive an implant.Referring further to FIGS. 2-3, and as also shown in FIGS. 6 and 7,milling instrument assembly 15 includes a housing assembly 16 at itsdistal end positionable adjacent disc space 208. Milling instrumentassembly 15 also includes a guide assembly 18 extending proximally fromhousing assembly 16. Guide assembly 18 extends between and is coupledwith a cutting assembly 120 and with housing assembly 16. Cuttingassembly 120 extends through housing assembly 16 and into disc space208.

[0027] There is shown a spinal column segment 200 including vertebrae202, 204, and 206. Disc space 208 is between vertebrae 202 and 204.Vertebra 202 has endplate 210, and vertebra 204 has endplate 212. Accessto disc space 208 is obtained by any known surgical technique and willnot be described in detail herein. With respect to the view of FIGS. 2and 4, the X axis represents the anterior to posterior direction, the Yaxis extends laterally, while the Z axis extends in the superior toinferior direction. As shown in FIGS. 2 and 4, milling instrumentassembly 15 has a longitudinal axis 70 that, when inserted for ananterior oblique approach to the disc space, extends obliquely to the Xaxis and also to the Y axis. Stated another way, the position oflongitudinal axis 70 can be obliquely oriented to the sagittal plane (Xaxis) and coronal plane (Y axis) of the patient.

[0028] Housing assembly 16 includes a housing 20 and a block 50removably mounted in the proximal end of housing 20. Housing 20 includesa distal portion 30 and a proximal portion 32. Proximal portion 32 caninclude a recess 34 to facilitate attachment of other instruments, suchas a guide tube, to housing 20. Block 50 is attached to proximal portion32. A passage or working channel 36 (FIG. 3) extends through housing 20,and extensions 22, 24 extend distally from distal portion 30 on eitherside of the passage or working channel 36. Housing 20 can include upperarcuate distal end surface 26 and lower arcuate distal end surface 28each adapted to contact or extend generally along the arcuate anterioroblique surfaces of the adjacent vertebra 204, 202 on either side ofdisc space 208.

[0029] Housing 20 can be provided with extensions 22, 24 extendingdistally therefrom adapted and configured to extend into disc space 208.Extensions 22 and 24 can each engage the endplates 210, 212 to maintainthe distraction obtained with a previously inserted distractor. It isalso contemplated that extensions 22, 24 can be self-distracting. It isfurther contemplated that extensions 22, 24 can be non-distracting. Eachof the extensions 22, 24 can be provided with an external taper on itsleading surface adapted to urge tissue to the exterior of the housingand away from the distal end opening of housing 20. Extensions 22, 24can also include bone engaging surfaces 23 that bite into or grip theadjacent vertebral endplate to inhibit dislodgment once positioned indisc space. Housing 20 retains its position in the disc space andadjacent the anterior portions of vertebrae 204 and 206 with extensions22 and 24 engaging end plates 210 and 212 to maintain the disc spaceheight and angulation established thereby or by previous distraction.Extension 22 can have a greater length than extension 24 for extensionto a greater depth in disc space 208, with each extension 22, 24 havinga length corresponding to the depth of cut to be made adjacent thereto.

[0030] Cutting assembly 120 includes a shaft 122 extending through adepth tube 90. Cutting assembly 120 includes a proximal portion 130proximal depth tube 90 and a cutting element 126 in disc space D.Cutting assembly 120 can be engaged with depth tube 90 by, for example,abutting enlarged shaft portion 128 against the proximal end of depthtube 90. When so engaged, cutting assembly 120 is not movable axially inthe distal direction in depth tube 90. Depth tube 90 abuttingly engagesblock 50 and moves along a guide surface extending across block 50,providing a controlled depth of cut in the proximal-distal direction indisc space 208 for cutting element 126. To facilitate movement of depthtube 90 across block 50, a linkage 80 extends around depth tube 90.Linkage 80 is coupled to a first connecting member 102 of guide housing100. Guide housing 100 includes a second connecting member 104 coupledto block 50. Linkage 80 and guide housing 100 move with depth tube 90across block 50 while maintaining cutting assembly 120 in parallelalignment with axis 70.

[0031] Referring now to FIG. 4, depth tube 90, and thus cutting assembly120, are guided across block 50 to provide a prepared endplate site 186formed by moving cutting element 126 along a length of a cutting path180 between a first side 188 and a second side 190 of prepared site 186.In FIG. 4, the endplate 210 of lower vertebra 202 is shown, it beingunderstood that endplate 212 of vertebra 204 would have a substantiallysimilar shape formed by the cutting element 126 positioned as shown inFIG. 3. Cutting path 180 includes a first portion 182 extendingorthogonally to longitudinal axis 70 of milling instrument assembly 15.Cutting path 180 further includes a second portion 184 that extendsobliquely to longitudinal axis 70.

[0032] In the illustrated embodiment, oblique second portion 184 iscurved or arcuate between first portion 182 and a second side 190. Theoblique second portion 184 can comprise about one half the length ofcutting path 180. It is contemplated that oblique portion 184 can rangefrom the entire length of cutting path 180 to about one-eighth of thelength of cutting path 180 or less. In another form, the oblique portioncomprises one-fourth to three fourths of the length of cutting path 180.It is also contemplated that second portion 184 can be linear, or acombination of linear and curved segments. It is further contemplatedthat the entire cutting path 180 can be obliquely oriented relative tolongitudinal axis 70.

[0033] Cutting path 180 is formed by moving cutting assembly 120side-to-side along across block 50 transversely to longitudinal axis 70.This moves cutting element 126 in the disc space along the adjacentvertebral endplate. Prepared site 186 has a first side 188 that has agreater length than a second side 190. This shorter second side 190 isformed by moving cutting element proximally as it is guided betweenfirst side 88 and second side 90. In this manner, cutting element 126 ismoved away from posterior elements of the vertebra, such as posteriorside 214 of vertebra 202. If cutting path 180 were entirely orthogonalto longitudinal axis 70, the extension of the cutting element into discspace 208 along first side 188 would have to be reduced to avoidposterior side 214 of vertebra 202, or the possible intrusion into theposterior elements with cutting element 126 would have to be tolerated.Accordingly, milling instrument assembly 15 allows cutting element 126to extend far into disc space 208 along first side 188, while cuttingelement 126 is moved away from the posterior elements of vertebra 214 ascutting element 126 is guided toward second side 190.

[0034] It is contemplated that housing 20 can then provide an accessport or window into disc space 208. It is also contemplate that a guideor retractor tube could be attached to housing 20 to facilitate discspace preparation and/or implant insertion into disc space 208. Forexample, block 50, guide assembly 18 and cutting assembly 120 could bepositioned in a guide tube during endplate preparation. After endplatepreparation, block 50, guide assembly 18 and cutting assembly 120 couldbe removed and the guide tube used to access the prepared disc space.

[0035] In FIG. 5 there is one embodiment of a guide tube 132 that isprovided with a substantially rectangular or square working channeladapted and configured to correspond with the proximal dimensions ofhousing 20. Also contemplated are guide tubes having working channelswith substantially circular, oval, figure-eight or any othercross-sectional configurations that may be utilized for disc spacepreparation and implant insertion. Guide tube 132 can be provided with afront flange 150 adapted to engage the proximal portion of housing 20.Guide tube 132 also includes retaining assembly 154 that may be utilizedto selectively couple guide tube 132 to housing 20. Retaining assembly154 includes an outer shaft 164 coupled to guide tube 132. An innershaft 160 extends along the length of outer tube 164. A finger lever 156is positioned at the proximal end of inner shaft 160, and a retainingfoot 158 is positioned at or near the distal portion of inner shaft 160.

[0036] Housing 20 may be coupled to guide tube 132 by initially bringingguide tube 132 into a butting engagement with housing 20 such thatflange 150 surrounds at least a portion of housing 20. Lever 156 maythen be rotated to cause retaining foot 158 to 20 rotate into recess 34on housing 20. With retaining foot 168 extending into recess 34, housing20 and guide tube 132 are removably coupled to one another. Guide tube132 and housing 20 may then be advanced over any inserted distractor orguided into position into the disc space with a centering element or thelike. The proximal end of guide tube 132 can be impacted or driventoward the disc space to advance distraction holders 22 and 24 into thedisc space. Once the guide tube and/or housing 20 have been properlypositioned, any inserted distractor or other instrument can be removedfrom the disc space leaving the guide tube and housing assembly inplace. When desired to remove guide tube 132, lever 156 of retainingassembly 154 may then be rotated in an upward direction thereby causingretaining foot 158 to rotate out of recess 34 of housing 20. Withretaining foot 158 positioned out of engagement with recess 34, guidetube 132 may be disengaged from housing 20.

[0037] Referring to FIGS. 6 and 7, there are shown further details ofmilling instrument assembly 15. Housing assembly 16 includes housing 20and block 50 removably mounted in the proximal end of housing 20.Housing 20 includes distal portion 30 and proximal portion 32 havingworking channel or passage 36 extending therethrough. Extensions 22, 24extend distally from distal portion 30 on either side of passage 36. Aprojection or spike 40 can extend distally from one or both of thedistal end surfaces 26, 28 for engagement with the adjacent vertebralbody.

[0038] Passage 36 can be sized in proximal portion 32 to receive adistal portion 52 of block 50 therein so that block 50 abuts againstproximal end 40 of housing 20. Proximal portion 54 of block 50 residesproximally of housing 20. Distal portion 52 can provide a substantiallyclose fit with the internal dimensions of proximal portion 32 of housing20 such that block 50 is not movable with respect to the housing 20 indirections other than proximally toward the user. It is contemplatedthat block 50 can be removably attached to housing 20 before and/orafter housing 20 has been positioned adjacent the spinal disc space.Block 50 can be attached with a friction or interference fit withhousing 20, or via one or more coupling mechanisms, such as a clip,fastener, ball-detent mechanism or other coupling mechanism. Otherembodiments contemplate that block 50 can be integral with housing 20.

[0039] It is further contemplated that housing 20 can be provided withan indicator receptacle 38 to receive indicator 51 (FIG. 8) of block 50when block 50 is properly positioned in housing 22. In this manner, thesurgeon is provided an indication of whether cutting assembly 120 ispositioned along the appropriate vertebral endplate since indicator 51will contact the proximal end of housing 20 and prevent proper seatingof block 50 therein unless indicator 51 is received in receptacle 38.For example, the illustrated embodiment shows a block 50 configured forpositioning cutting assembly 120 along the upper vertebral endplate. Asecond block could be provided for attachment to housing 20 andconfigured for positioning cutting assembly 120 along the lowervertebral endplate. The first and second blocks would not properly seaton housing 20 unless indicator 51 was received in receptacle 38,orienting the cutting element along the appropriate upper or lowervertebral endplate.

[0040] Block 50 includes a proximal face 64 having a slot 56 formedtherein. Slot 56 includes a through-way 60 extending therethrough incommunication with passage 36. A guide surface 58 extends aboutthrough-way 60, and, as discussed further below, forms a guide surfacealong which cutting assembly 120 is guided with guide assembly 18 forendplate preparation along cutting path 180. It is further contemplatedthat slot 56 of block 50 can be configured for preparing the vertebralendplates in a manner that establishes and/or maintain angulationbetween adjacent vertebra relative to the axial plane. For example, asshown in FIG. 9, upper surface 72 and lower surface 74 of slot 56 can bedisposed at an angle 68 with respect to the longitudinal axis 70 ofhousing assembly 16. In the illustrated embodiment, longitudinal axis 70extends parallel to the axial plane of the patient.

[0041] Instrument assembly 15 further includes guide assembly 18 adaptedto guide cutting assembly 120 across housing assembly 16 during endplatepreparation. Guide assembly 18 includes a guide housing 100 mountable onmounting post 62 and a linkage 80 extending between and coupling guidehousing 100 with cutting assembly 120. Linkage 80 includes a guide tube82 having a passage 84 extending therethrough. A connecting portion 86extends between and connects linkage post 88 with guide tube 82.Connecting portion 86 can be integrally formed with guide tube 82 andlinkage post 88, although separable and/or rigidly attached componentsare also contemplated for linkage 80.

[0042] Guide housing 100 includes a first connecting member 102 and asecond connecting member 104. First connecting member 102 includes apassage 106 sized to receive linkage post 88 of linkage 80 therein, andsecond connecting member 104 includes a passage 108 sized to receivemounting post 62 of block 50 therethrough. First and second connectingmembers 102, 104 extend alongside one another, and can be integrallyformed with one another or separable but rigidly attached components.When assembled, first connecting member 102 is adjacent connectingportion 86 of linkage 80 and second connecting member 104 is adjacentproximal face 64 of block 50. A fastener 110 is engageable in recess 63extending about mounting post 62 to secure guide housing 100 to mountingpost 62. Fastener 110 can be a snap ring, crimpable ring, cotter pin, orother fastener capable of securing mounting post 62 to guide housing100.

[0043] It is contemplated block 50 can be angled with respect to thelongitudinal axis 70 to permit end plate cutting and preparation at anangle desirable to maintain and/or establish an angular relationshipbetween adjacent vertebrae. For example, as shown in FIG. 8, proximalface 64 can be set at a corresponding angle 66 with respect to an axis76 extending orthogonally to longitudinal axis 70. It will be understoodthat the angulation of proximal face 64 provides proximal portion 54with a taper from bottom surface 57 to a lesser thickness at uppersurface 55. Thus, proximal face 64 can provide a reference plane for theattachment of other guiding elements such that they may be maintained inthe proper angular relationship with the angle of slot 56. It is furthercontemplated that mounting post 62 can be centrally located between thesidewalls of distal portion 54 below slot 56, and extend from proximalface 64 at angle 68 relative to longitudinal axis 70. It is alsocontemplated that upper and lower surfaces 72, 74 for slot 56 and/ormounting port 62 can extend substantially parallel to longitudinal axis70.

[0044] Guide assembly 18 further includes depth tube 90. Depth tube 90includes a passage 96 sized to receive at least a portion of cuttingassembly 120 therein. The proximal end 98 of depth tube 90 can contactan enlarged portion 128 along shaft 122 of cutting assembly 120 to limitdistal movement of cutting assembly 120 relative to depth tube 90. Depthtube 90 includes a distal end 91 and an enlarged distal portion 92residing within slot 56. Distal end 91 can be chamfered, tapered or havea spherical shape to reside in abutting engagement with acorrespondingly shaped guide surface 58 extending around through-way 60.Depth tube 90 extends through guide tube 82 of linkage 80. Guide tubeportion 82 includes an internal lip 86 extending radially into passage84. Lip 86 is engageable with enlarged portion 92 to limit proximalmovement of depth tube 90 in guide tube 82.

[0045] Guide assembly 18 is assembled by placing guide tube 82 arounddepth tube 90 and depth tube 90 around the shaft of cutting assembly120. First connecting member 102 of guide housing 100 is positioned overlinkage post 84 of linkage 80. Second connecting member 104 is placedover mounting post 62 with distal end 91 of depth tube 90 positioned inslot 156. Cutting element 126 can be mounted on distal portion 124 ofshaft 122 extending into passage 36, and fastener 110 placed around theproximal end of mounting post 62 to secure guide housing 100.Alternatively, if cutting element 126 were integral with shaft 122,proximal portion 130 can be attached to shaft 122 after insertion ofshaft 122 proximally through the distal ends of housing assembly 16 anddepth tube 90.

[0046] Guide housing 100 is rotatable about mounting post 62 and linkagepost 84, and guide tube 82 is rotatable about depth tube 90. Thisinterconnection between block 50 and cutting assembly 120 permitsmovement of depth tube 90 along slot 56 with its distal end 91 inabutting engagement with guide surface 58. As shown in FIG. 8, depthtube 90 and guide tube portion 82 can be disposed at an angle 68 withrespect to the longitudinal axis 70 of milling instrument assembly 15.Thus, depth tube 90 is in substantial alignment with the upper and lowersurfaces 72, 74 of slot 56 and will be maintained in substantialalignment throughout the cutting process. Enlarged distal portion 92 cansnugly fit within slot 56 to provide precise guiding of the cuttingelement 126 along guide surface 58 and limit or prevent movement ofcutting element 126 relative to the axial plane or in the direction ofthe Z axis. As shown in FIGS. 9-12, distal end 91 of depth tube 90engages guide surface 58 of slot 56 to limit the distal axial extentcutting element 126 may extend within passage 36. Furthermore, enlargedportion 128 of shaft 122 abuts the proximal end 98 of depth tube 90 tolimit the distal axial extent cutting element 126 can move relative todepth tube 90.

[0047] Guide assembly 18 and block 50 may be coupled with housing 20 sothat cutting element 126 extends into passage 36 between extensions 22,24. Cutting element 126 can be a burr with a cutting bit configured toengage and cut exposed vertebral bone or other tissues of the adjacentvertebral endplate with reciprocating or rotational motion as it ismoved along guide surface 58. It is contemplated that proximal portion130 can include a handle and/or a coupler for attachment to a powersource to drive cutting element 126. Other cutting elements and drivemeans are also contemplated, including hand operated instruments, may beutilized in combination with housing assembly 16 and guide assembly 18.

[0048] As shown in FIGS. 9-12, cutting path 180 extends parallel toguide surface 58 so that cutting element 126 is guided along cuttingpath 180 obliquely to longitudinal axis 70 of milling instrumentassembly 15. Distal end 91 of depth tube 90 abuts guide surface 58 atthe first side of slot 56, as shown in FIGS. 9, 11 and 13, where cuttingelement 126 extends along extension 22. Depth tube 90 and guide tube 82are movable transversely to longitudinal axis 70 along guide surface 58in slot 56 to position cutting element 126 of cutting assembly 120adjacent extension 24, as shown in FIGS. 10, 12 and 14. Depth tube 90and guide tube 82 can also be moved in the opposite direction fromsecond extension 24 to first extension 22 while cutting with cuttingelement 126. The distal depth of cut can correspond to the depthextensions 22, 24 extend into the disc space.

[0049] At least a portion 59 of guide surface 58 extends proximallywithin slot 56 relative to the remaining portion of guide surface 58such that portion 59 is obliquely oriented relative to longitudinal axis70. In the illustrated embodiment, oblique portion 59 of guide surface58 defines a curved or arcuate path that is followed by cutting path180. Other embodiments contemplate linear paths, or combined linear andarcuate paths. along the oblique portion 59 of guide surface 58. Theoblique portion 59 moves cutting assembly 120 and depth tube 90proximally in slot 56 as they move together toward second extension 24.Depth tube 90 and cutting assembly 120 also move proximally in guidetube 82 as they move together toward second extension 24. This directscutting element 126 and thus cutting path 180 proximally in the discspace and away from the spinal canal and posterior elements of thevertebra as discussed above.

[0050] In the illustrated embodiment, oblique portion 59 is curved orarcuate. The oblique portion 59 can comprise about one half the lengthof guide surface along slot 56. It is contemplated that oblique portion59 can range from the entire length of slot 56 to about one-eighth ofthe length of slot 56 or less. In another form, the oblique portion 59comprises one-fourth to three fourths of the length of slot 56.

[0051] Housing assembly 16 and guide assembly 18 provide controlledcutting of non-angular or angular surfaces, with the cut beingsubstantially maintained over a large lateral distance defined by, forexample, slot 56. Housing assembly 16 and guide assembly 18 not onlymaintain the vertical angulation of the cutting instrument but alsomaintain the cutting instrument in a substantially fixed side-to-siderange of movement between extensions 22, 24, limiting the potential foraccidental penetration into tissues along the lateral extent of the discspace. Further, housing assembly 16 and guide assembly 18 limit theanterior-posterior depth of cutting element 126 as it moves from a firstdepth in the disc space along one side of the housing assembly to asecond, lesser depth in the disc space along the other side of thehousing assembly, and back.

[0052] It is contemplated that kits could be provided with blocksallowing varying incremental bone removal to provide the ability toadjust endplate preparation depths without removal of housing 20 fromthe disc space. Furthermore, in the illustrated embodiment, a block andguide assembly for preparation of the upper vertebral endplate has beendisclosed, it being understood that a similarly configured block andguide assembly can be provided for substantially similar preparation ofthe lower vertebral endplate. Furthermore, in the illustratedembodiment, a block and guide assembly for preparation of the vertebralendplate from a right-handed (relative to the surgeon) anterior obliqueapproach has been disclosed. It is to be understood that a similarlyconfigured block and guide assembly can be provided for substantiallysimilar preparation of the endplate from a left-handed anterior obliqueapproach. It is further contemplated that the instruments can be used indirect anterior, anterior offset lateral and other approaches to thedisc space in which an obliquely oriented cutting path may be desired.

[0053] In one surgical procedure, the disc space is accessed from ananterior oblique approach. Disc material can be removed, and the discspace distracted to the desired disc space height between the adjacentvertebrae. It is contemplated that housing 20 can be inserted over oneor more disc space distractors already inserted in the disc space, orinserted directly into the disc space. It is further contemplated that aguide tube, such as guide tube 132 can be removably attached to theproximal end of housing 20 either before or after insertion thereof. Theguide tube can have a working channel to slidingly receive the proximalend of housing 20 therein. Block 50, guide assembly 18 and cuttingassembly 120 can be inserted through the guide tube for attachment withhousing 20, or attached to housing 20 with guide tube removed.

[0054] After the disc space has been prepared, including removal of adesired amount of bone from the vertebral endplates at the desired angleand depth with milling instrument assembly 15, block 50, guide assembly18 and cutting assembly 120 can be removed from housing 20. The guidetube can be reattached, if desired, to housing 20. An implant can beinserted through the guide tube and housing 20 into the prepared discspace. It is contemplated that the implant can be an interbody spacer,interbody fusion device, artificial disc or other intervertebralimplant. The implant can be made from bone material or syntheticmaterial. The housing and any attached guide tube can then be removed.

[0055] While guide surface 58 has been shown in slot 56, other locationsfor guide surface 58 are contemplated. For example, guide surface 58could be formed along a projecting extending proximally from block 50,along the proximal face 64 of block 50, or in housing 20.

[0056] While the invention has been illustrated and described in detailin the drawings and foregoing description, the same is to be consideredas illustrative and not restrictive in character, it being understoodthat all changes and modifications that come within the spirit of theinvention are desired to be protected.

What is claimed is:
 1. An instrument for preparation of an endplate of avertebra of a spinal column, comprising: a housing positionable adjacentthe vertebra; a block proximal said housing; and a cutting assemblyextending through said block and into said housing, wherein theinstrument defines a longitudinal axis extending from the vertebra whenthe housing is positioned adjacent the vertebra, said cutting assemblybeing guidable across said block along a cutting path on the endplateextending transversely to said longitudinal axis, at least a portion ofsaid cutting path being obliquely oriented to said longitudinal axis. 2.The instrument of claim 1, wherein said block includes a guide surfaceextending parallel to said cutting path and said cutting assembly isguidable along said guide surface.
 3. The instrument of claim 2,wherein: said block includes a slot formed in a proximal face thereof;said slot includes a through-way in communication with said housing; andsaid guide surface extends about said slot.
 4. The instrument of claim2, wherein said guide surface includes a first portion extendingtransversely to said longitudinal axis and a second portion obliquelyoriented to said longitudinal axis.
 5. The instrument of claim 1,further comprising a guide assembly linking said cutting assembly andsaid block.
 6. The instrument of claim 5, wherein said guide assembly isadapted to guide said cutting assembly in a slot formed in said block,said slot having a guide surface extending parallel to said cuttingpath.
 7. The instrument of claim 5, wherein said guide assemblyincludes: a depth tube receiving said cutting assembly; and a guide tubereceiving said depth tube, wherein said guide tube and said depth tubeare movable together transversely to said longitudinal axis along aproximal face of said block and said depth tube is further axiallymovable relative to said guide tube along a guide surface of said blockfollowing said cutting path.
 8. The instrument of claim 7, wherein saidguide tube includes a proximal lip engaging an enlarged portion of saiddepth tube to limit axial proximal movement of said depth tube in saidguide tube.
 9. The instrument of claim 7, wherein said cutting assemblyincludes a shaft having an enlarged portion engaging a proximal end ofsaid depth tube to limit axial distal movement of said cutting assemblyin said depth tube.
 10. The instrument of claim 5, wherein said guideassembly angles said cutting assembly relative to an axial plane of thespinal column to cut an axially angled surface on the endplate of thevertebra.
 11. The instrument of claim 5, wherein: said guide assemblyincludes a depth tube receiving said cutting assembly therethrough and aguide tube having a through channel adapted to receive said depth tube,said guide tube and said depth tube movable together across said block;and said block includes a slot formed therein with a guide surfaceextending generally parallel to said cutting path and said depth tubeincluding a distal end in abutting engagement with said guide surface,wherein said depth tube is movable along said guide surface andsimultaneously axially movable relative to said guide tube therebymoving said cutting assembly along said cutting path.
 12. The instrumentof claim 11, wherein said guide assembly includes a linkage couplingsaid guide tube to said block.
 13. The instrument of claim 1, whereinsaid cutting assembly includes a burr cutting element at a distal endthereof.
 14. The instrument of claim 1, wherein said housing is adaptedfor insertion in a disc space adjacent the vertebra from an anterioroblique approach to the vertebra.
 15. The instrument of claim 1, whereinsaid portion of said cutting path is arcuate.
 16. The instrument ofclaim 1, wherein said cutting path includes a second portion extendingorthogonally to said longitudinal axis and said obliquely orientedportion of said cutting path extends proximally from said secondportion.
 17. The instrument of claim 1, wherein said housing includes apair of opposite distraction flanges extending therefrom andpositionable in a disc space adjacent the vertebra.
 18. The instrumentof claim 1, wherein said portion of said cutting path comprises abouthalf of said cutting path.
 19. The instrument of claim 1, wherein saidlongitudinal axis extends obliquely to a sagittal plane of the spinalcolumn in an anterior oblique direction.
 20. An instrument forpreparation of an endplate of a vertebra of a spinal column, comprising:a housing assembly positionable adjacent the vertebra; and a cuttingassembly extendable through said housing assembly, wherein theinstrument defines a longitudinal axis extending from the vertebra whensaid housing assembly is positioned adjacent the vertebra, wherein saidcutting assembly is transversely guidable along a guide surface of saidhousing assembly, at least a portion of said guide surface beingobliquely oriented to said longitudinal axis.
 21. The instrument ofclaim 20, wherein said housing assembly includes a housing positionableadjacent the vertebra and a block engaged to and extending proximallyfrom said housing.
 22. The instrument of claim 20, further comprising aguide assembly pivotally linking said cutting assembly and said housingassembly.
 23. The instrument of claim 22, wherein said guide assembly isadapted to guide said cutting assembly in a slot formed in said housingassembly, said guide surface extending along said slot.
 24. Theinstrument of claim 22, wherein said guide assembly includes: a depthtube receiving said cutting assembly; and a guide tube receiving saiddepth tube, wherein said guide tube is movable orthogonally to saidlongitudinal axis along a proximal face of said housing assembly andsaid depth tube is movable with said guide tube with said depth tube inabutting engagement with said guide surface and said depth tube isfurther axially movable relative to said guide tube to follow said guidesurface as said depth tube moves therealong.
 25. The instrument of claim23, wherein said slot includes a through-way and said guide surfaceextends about said through-way.
 26. The instrument of claim 22, whereinsaid guide assembly is constructed and arranged to guide said cuttingassembly along said guide surface.
 27. The instrument of claim 22,wherein said guide assembly includes a linkage coupling said cuttingassembly to said housing assembly.
 28. The instrument of claim 20,wherein said cutting assembly includes a burr cutting element at adistal end thereof.
 29. The instrument of claim 20, wherein saidlongitudinal axis extends obliquely to a sagittal plane of the spinalcolumn in an anterior oblique direction.
 30. An instrument forpreparation of an endplate of a vertebra of a spinal column, comprising:a housing assembly positionable adjacent the vertebra; and a cuttingassembly extending through said housing assembly, wherein the instrumentdefines a longitudinal axis extending from the vertebra when saidhousing assembly is positioned adjacent the vertebra; and means forguiding said cutting assembly relative to said housing assembly along acutting path extending transversely to said longitudinal axis, at leasta portion of said cutting path being obliquely oriented to saidlongitudinal axis.
 31. The instrument of claim 30, wherein said housingassembly includes a housing positionable adjacent the vertebra and ablock engaged to and extending proximally from said housing.
 32. Theinstrument of claim 30, wherein said means for guiding includes a guideassembly having a linkage coupling said cutting assembly to said housingassembly.
 33. The instrument of claim 32, wherein said guide assembly isadapted to guide said cutting assembly in a slot in said housingassembly, said slot having a guide surface extending parallel to saidcutting path.
 34. The instrument of claim 33, wherein said means forguiding includes: a depth tube receiving said cutting assembly; and aguide tube receiving said depth tube, wherein said guide tube is movableorthogonally to said longitudinal axis along a proximal face of saidhousing assembly and said depth tube is movable with said guide tubealong a guide surface in said housing assembly and is further axiallymovable relative to said guide tube to follow said guide surface as saiddepth tube moves therealong.
 35. The instrument of claim 34, whereinsaid guide surface is formed along a slot in said housing, said slotincluding a through-way and said guide surface extends about saidthrough-way.
 36. The instrument of claim 30, wherein said cuttingassembly is a burr assembly.
 37. The instrument of claim 30, whereinsaid portion of said cutting path comprises about half of said cuttingpath.
 38. The instrument of claim 30, wherein said longitudinal axisextends obliquely to a sagittal plane of the spinal column in ananterior oblique direction.
 39. An instrument for preparation of anendplate of a vertebra of a spinal column, comprising: a housingassembly positionable adjacent the vertebra; and a cutting assemblyextendable through said housing assembly; a guide assembly coupling saidcutting assembly to said housing assembly, wherein the instrumentdefines a longitudinal axis from the spinal column when said housingassembly is positioned adjacent the vertebra; and said guide assemblybeing transversely movable relative to said longitudinal axis along aguide surface of said housing assembly to move said cutting assemblytransversely along a cutting path, at least a portion of said guidesurface and said cutting path being obliquely oriented to saidlongitudinal axis.
 40. The instrument of claim 39, wherein saidlongitudinal axis extends obliquely to a sagittal plane of the spinalcolumn in an anterior oblique direction.
 41. A method for preparingendplates of adjacent vertebrae for insertion of an implant in a discspace between the adjacent vertebrae, comprising: accessing the discspace along an axis that extends generally in an anterior obliquedirection relative to a sagittal plane of the adjacent vertebrae;milling at least one endplate in side-to-side movement along a pathhaving at least a portion obliquely oriented to the axis.
 42. The methodof claim 41, wherein the path includes a portion orthogonally orientedto the axis.
 43. The method of claim 41, wherein the portion of the pathobliquely oriented to the axis is arcuate.
 44. The method of claim 41,further comprising distracting the adjacent vertebrae.
 45. The method ofclaim 41, further comprising inserting an implant in the disc space.